This invention relates in general to the manufacture of cast metal components and in particular to an apparatus and method for reclamation of metal chips which are produced when the components are machined to final shape.
Metal components, such as vehicle wheels cast from alloys of light weight metals, are typically produced in high volumes on highly automated production lines. Such production lines include a melt furnace for melting metal stock. A casting machine which typically includes a plurality of molds is located adjacent to the melt furnace. The molds are sequentially filled with molten metal from the melt furnace to form rough castings. After the rough castings have cooled sufficiently, they are removed from the molds, allowing the molds to be filled again.
The rough castings are machined to a final shape. The machining typically includes a plurality of discrete operations, such as drilling, boring, turning and facing. The machining operations are usually performed at multi-tool computer-controlled machining stations. To aid the machining operation, the cutting tool is usually sprayed with a cooling and lubricating fluid as the metal is being cut. The components also may be painted and/or given a clear coating between machining operations.
As the rough casting is machined to the final shape, small pieces, or "chips", of metal are cut from the casting surface. Depending upon the component being manufactured, a significant amount of chips can be produced. For example during the machining of a typical vehicle wheel, as much as eight pounds of chips can be produced. It is desirable to reclaim the metal chips by collecting and melting them for use in casting additional components.
A typical known reclamation system for collecting and remelting metal chips is shown generally at 10 in FIG. 1. FIG. 1 is a block diagram which shows the flow of metal chips through the system 10. Metal chips are produced by a plurality of machining operations, two of which, 11 and 12, are shown. As described above, the metal chips are typically contaminated with cutting and cooling fluid and may be coated with paint.
The chips are collected and moved to a central chip processing facility 13. The chip collection and movement can be continuous with conventional material handling equipment such as conveyor belts or pneumatic conveyors linking the individual machine machining operations 11 and 12 to the central chip processing facility 13. Alternately, the chips can be accumulated in individual bins located adjacent to each machining operation and periodically collected and transported to the chip processing facility 13.
The central chip processing facility 13 typically includes a centrifuge and rotary drum kiln. The centrifuge removes excess water and oil from the chips. The kiln dries the chips and burns contaminants off the chip surfaces. The dried chips are deposited in a chip storage hopper 14.
The dried metal chips are transferred from the storage hopper 14 to a remelt furnace 15, which is dedicated to melting the chips. The remelt furnace 15 is typically a conventional reverbratory furnace having a central chamber which is heated by combustion burners fueled with oil or natural gas. Metal stock is melted in the central chamber to form a pool of molten metal. An open charge well and circulation well extend from the central chamber and contain a portion of the molten metal. The charge well receives the metal chips for melting while the circulation well allows removal of molten metal from the furnace. Because of the large volume of chips being processed by the remelt furnace 15, it is common to include a circulation pump which continuously moves the molten metal between the central chamber and the charge and circulation wells.
If the dried chips are simply thrown or otherwise deposited upon the surface of the molten metal in the remelt furnace charge well, the chips will disturb the metal oxide skin, or dross, which normally exists on top of the molten metal. The disturbance of the metal oxide skin results in the agglomeration of many of the metal chips into the metal oxide skin. Accordingly, only a small portion of the metal chips actually sink into the molten metal and are melted.
The chips which are agglomerated are not submerged in the molten metal, but are raised in temperature by the molten metal. Because they are in the presence of oxygen, the agglomerated chips are oxidized and are absorbed into the dross. The dross is periodically removed from the furnace and discarded. Thus, the chips which are oxidized are lost. Additionally, while the chips are being oxidized, any surface contaminates remaining on the chips are burned off, releasing fumes into the workplace.
In order to assure that the chips are melted, the dried metal chips are loaded into the remelt furnace with a chip charger 16. The chips are batch loaded into the chip charger 16 which then inserts the chips below the surface of the molten metal in the remelt furnace 15.
Known chip chargers 16 are typically complex devices. One known chip charger, as disclosed in U.S. Pat. No. 4,702,768, includes an chip compactor and strip forming apparatus to extrude the chips into stripform metal. The stripform metal is then forced below the surface of the molten metal.
Another known chip charger, as disclosed in U.S. Pat. No. 4,872,907, includes a tube which has one end inserted below the surface of the molten metal. A helical auger compacts the metal chips and forces the compacted chips through the tube and into the charge well. Upon exiting the delivery tube, the compacted chips dissociate from one another and are immediately melted. A charge well cover, which is disclosed in U.S. Pat. No. 5,211,744, covers a substantial portion of the surface of the molten metal and is in contact, or close proximity, therewith to further prevent oxidation of the chips. A mechanism is included which raises and lowers the cover as the level of the molten metal varies to maintain the contact therebetween.
After the chips are melted, molten metal can be drawn from the remelt furnace 15 and placed into ladles (not shown). The ladles are transported, as shown by the dashed lines in FIG. 1, to charge a plurality of individual production line melt furnaces, two of which, labeled as 17 and 18, are shown in FIG. 1. The molten metal is poured from the ladles into the melt furnaces. Alternately, the reclaimed metal chips can be cast into ingots, or "sows". The sows are transported to the melt furnaces for melting. Molten metal, which includes the melted metal chips, is drawn from the melt furnaces 17 and 18 to supply casting machines 19 and 20.
The known reclamation system 10 illustrated in FIG. 1 has several shortcomings. The system 10 batch loads metal reclaimed from the chips into the melt furnaces. This decreases the ratio in the melt furnaces between primary melt of new stock and chips. Some applications, such as casting vehicle wheels, require that a high ratio be maintained. While the reclamation system 10 removes the majority of oil and paint, a small amount remains on the chips. The chip stream can also include dirt and particles of other metal, such as steel from the tools used in the machining operations. These materials contaminate the molten metal in the melt furnaces. Accordingly, a minimum value for the ratio of new stock to chips is specified to maintain the quality of the castings. The batch loading of the reclaimed metal chips also can excessively reduce the temperature of the molten metal, causing crystallization or solidification thereof.
Additionally, the transport of molten metal between the remelt furnace 16 and the individual production line melt furnaces 17 and 18 posses a safety concern. The transport also would require additional manpower. Furthermore, the use of a central furnace 32 solely dedicated to melting metal chips is inefficient, requiring additional energy to maintain the melted chips.
Accordingly, it would be desirable to continuously deliver chips directly to the individual melt furnaces 17 and 18 for melting. However, the cost of installing a prior art chip charger on each melt furnace would be very high.